<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <style>
        .exciting-text::after {
            content: "<- 让人兴兴兴奋!";
            color: green;
        }

        .boring-text::after {
            content: "<- 无聊!";
            color: red;
        }
    </style>
</head>
<body>
<p class="boring-text">这是些无聊的文字</p>
<p>这是不无聊也不有趣的文字</p>
<p class="exciting-text">在MDN上做贡献简单又轻松。
    按右上角的编辑按钮添加新示例或改进旧示例！</p>
</body>
</html>